Caterpillars

Butterfly larvae, or caterpillars, consume plant leaves and spend practically all of their time in search of food. Although most caterpillars are herbivorous, a few species such as Spalgis epius and Liphyra brassolis are entomophagous (insect eating). Some larvae, especially those of the Lycaenidae, form mutual associations with ants. They communicate with the ants using vibrations that are transmitted through the substrate as well as using chemical signals.[5][6] The ants provide some degree of protection to these larvae and they in turn gather honeydew secretions. Caterpillars mature through a series of stages called instars. Near the end of each instar, the larva undergoes a process called apolysis, in which the cuticle, a tough outer layer made of a mixture of chitin and specialized proteins, is released from the softer epidermis beneath, and the epidermis begins to form a new cuticle beneath. At the end of each instar, the larva moults the old cuticle, and the new cuticle expands, before rapidly hardening and developing pigment. Development of butterfly wing patterns begins by the last larval instar. Butterfly caterpillars have three pairs of true legs from the thoracic segments and up to 6 pairs of prolegs arising from the abdominal segments. These prolegs have rings of tiny hooks called crochets that help them grip the substrate.[7] Some caterpillars have the ability to inflate parts of their head to appear snake-like. Many have false eye-spots to enhance this effect. Some caterpillars have special structures called osmeteria which are everted to produce foul-smelling chemicals. These are used in

efense. Host plants often have toxic substances in them and caterpillars are able to sequester these substances and retain them into the adult stage. This makes them unpalatable to birds and other predators. Such unpalatibility is advertised using bright red, orange, black or white warning colours, a practice known as aposematism. The toxic chemicals in plants are often evolved specifically to prevent them from being eaten by insects. Insects in turn develop countermeasures or make use of these toxins for their own survival. This "arms race" has led to the coevolution of insects and their host plants. Aposematism (from apo- away, and semantic sign/meaning), perhaps most commonly known in the context of warning coloration, describes a family of antipredator adaptations where a warning signal is associated with the unprofitability of a prey item to potential predators.[1] It is one form of "advertising" signal, with many others existing, such as the bright colours of flowers which lure pollinators. The warning signal may take the form of conspicuous colours, sounds, odours[2] or other perceivable characteristics. Aposematic signals are beneficial for both the predator and prey, both of which avoid potential harm. This tendency to become highly noticeable and distinct from harmless organisms is the antithesis of crypsis, or avoidance of detection. Aposematism has been such a successful adaptation that harmless organisms have repeatedly evolved to mimic aposematic species, a pattern known as Batesian mimicry. Another related pattern is Mullerian mimicry, where aposematic species come to resemble one another.